Synthesis of Pyrochlore‐Free 0.9Pb(Mg_1/3Nb_2/3)O₃‐0.1PbTiO₃ Ceramics via a Soft Mechanochemical Route

Abstract

Single-phase perovskite 0.9Pb(Mg 1/3 Nb 2/3 )O 3 -0.1PbTiO 3 The solid solution 0.9Pb(Mg 1/3 Nb 2/3 )O 3 -0.1PbTiO 3 (0.9PMN-(0.9PMN-0.1 PT) from a stoichiometric mixture of starting 0.1 PT) is one of the most widely investigated relaxor ferromaterials was synthesized by applying a mechanochemical electrics, because of its high dielectric constant and outstanding technique to the stage of a precursor. A stoichiometric mixelectrostriction near room temperature. 16 Preparation of ture of PbO, TiO 2 , Mg(OH) 2 , and Nb 2 O 5 was milled for 60 0.9PMN-0.1 PT solid solution, as well as PMN, is difficult, min and heated at temperatures as low as 850؇C for 4 h to however, because of the persistence of the second phase, pyroobtain a single phase. The maximum dielectric constant of chlore, which severely degrades the dielectric properties. Sevthe samples from the milled mixture increased as the sintereral attempts have been made to avoid the formation of ing temperature increased, with the remarkable grain pyrochlore phase. 17-20 Complete elimination of pyrochlore is growth, and attained 24600 at 1200؇C. In contrast, poor very difficult, however, mainly because of the evaporation of densification and coexistence of the pyrochlore phase werePbO. An addition of excess PbO 21,22 or MgO 23 reduces pyroobserved on the samples from the nonmilled mixture. Furchlore formation, but the resulting perovskite PMN is often ther observation suggested that the pyrochlore phase connonstoichiometric, with poor dielectric properties. 24,25 centrated near the surface during sintering and then A columbite precursor method, 26 by reacting a slight excess migrated into the PbZrO 3 packing powder, leading to a of MgO with Nb 2 O 5 and then with PbO, results in better repropyrochlore-free phase at 1250؇C. The dielectric constant of ducibility of PMN formation with a very low pyrochlore conthe latter ceramics was explained by the series mixing rule tent. However, it requires a series of complex reaction steps. for the dielectric constant of a diphasic solid.One of the nonconventional mixed-oxide processes, as an alternative, i.e., the KCl molten salt method, 27 forms single-phase PMN as well as PMN-PT powder. However, the removal of I. IntroductionKCl is not very easy. Another attempt was made, with a careful A MECHANOCHEMICAL technique serves the formation of pre-choice of the starting raw materials and wet attrition milling. 28 cursors of complex oxides for advanced ceramics. 1 The Pyrochlore-free PMN was formed from a mixture of PbO method has a wide application to synthesize complex oxides (massicot), Mg(CO) 3 , and monoclinic Nb 2 O 5 by heating at a from metallic, covalent, or ionic compounds. 2 Based on a simitemperature of 800ЊC for 5 h. In contrast, the pyrochlore phase lar concept, mechanical alloying technology is applied for remained in the case of a mixture from MgO instead of producing composite metal powders with a controlled fine Mg(CO) 3 at the same heating condition. The difference is microstructure. 3,4 explained by the higher ...

Hallmarks of mechanochemistry: from nanoparticles to technology

“…Phase-pure ilmenite MgTiO 3 with its quality factor (Q) as high as 9800 was obtained from a co-milled stoichiometric mixture of Mg(OH) 2 and TiO 2 . 543 A solid solution, 0.9Pb(Mg 1/3 Nb 2/3 )O 3 Â 0.1PbTiO 3 (0.9 PMN Â 0.1 PT) was obtained in a pure perovskite phase by starting from a co-milled stoichiometric mixture of PbO, TiO 2 , Mg(OH) 2 and Nb 2 O 5 by calcining at 850 1C for 4 h. 544 The maximum dielectric constant of 24 600 was attained after sintering at 1200 1C. A similar technique was applied to the more challenging system of a PMN-PZN solid solution to obtain phase-pure perovskite as well.…”

Preparations and characterizations of perovskite 0.80PMN–0.20PT ceramic by using a one-step calcination method

“…Swartz and Shrout [8] obtained PMN in high yield by using a columbite route, in which MgO and Nb 2 O 5 are first reacted to synthesize columbite phase (MgNb 2 O 6 ), followed by the reaction with PbO to synthesize perovskite phase. Several other processing methods have also been able to eliminate the formation of pyrochlore phase in powders, including sol-gel, solution processes, co-precipitation, soft mechanochemical pulverization, Mg(NO 3 ) 2 mixing, molten salt method, and thermal spray methods [9][10][11][12][13][14][15].…”

Combustion synthesis of lead oxide nanopowders for the preparation of PMN–PT transparent ceramics

“…Compared to single-crystals which are difficult to grow for these compositions [11], ceramics can be easily hot-pressed or sintered in a variety of sizes and shapes with a high degree of optical uniformity on a macroscopic scale. Soft mechanochemical pulverization [12], sol-gel method [13], chemical co-precipitation method [14], B-site precursor method [15] have been reported for synthesis of PMN-PT ceramics. Conventionally, PMN-PT powder has been synthesized by the solid-state mixed oxides method [16][17][18].…”